U.S. patent number 8,391,225 [Application Number 12/721,417] was granted by the patent office on 2013-03-05 for frame based, on-demand spectrum contention destination resolution.
This patent grant is currently assigned to STMicroelectronics, Inc.. The grantee listed for this patent is Wendong Hu. Invention is credited to Wendong Hu.
United States Patent |
8,391,225 |
Hu |
March 5, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Frame based, on-demand spectrum contention destination
resolution
Abstract
A method and system by which a base station in a Wireless
Regional Area Network (WRAN), and more generally a transceiver in a
cognitive radio (CR) system, can communicate with other
transceivers to fairly share transmission and reception of
scheduled use ("occupancy") of frames on a single channel within a
frame-based, on demand spectrum contention system. The method and
system disclose how the base station currently occupying a channel
responds to requests from other base stations for an increased
share of the frames available in a subsequent superframe of the CR
system. The method and system assure fair and efficient access to
the transmission channel by a random number based contention
process.
Inventors: |
Hu; Wendong (San Jose, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hu; Wendong |
San Jose |
CA |
US |
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Assignee: |
STMicroelectronics, Inc.
(Coppell, TX)
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Family
ID: |
42730631 |
Appl.
No.: |
12/721,417 |
Filed: |
March 10, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100232361 A1 |
Sep 16, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61158855 |
Mar 10, 2009 |
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Current U.S.
Class: |
370/329; 370/447;
370/350; 370/462; 370/338; 455/509; 455/450; 370/461; 455/524 |
Current CPC
Class: |
H04W
72/0426 (20130101); H04W 74/0808 (20130101); H04W
72/0406 (20130101); H04W 16/14 (20130101) |
Current International
Class: |
H04W
4/00 (20090101); H04B 7/26 (20060101); H04L
12/413 (20060101); H04J 3/06 (20060101) |
Field of
Search: |
;370/329,338,350,447,461,462 ;455/450,509,524 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10-2008-0067290 |
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Jul 2008 |
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KR |
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WO2010005262 |
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Jan 2010 |
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WO |
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Other References
Carlos Cordeiro, et al., "IEEE 802.22: An Introduction to the First
Wireless Standard based on Cognitive Radios", Philips Research
North America/Wireless Communication and Networking Dept.,
Briarcliff Manor, USA, Qualcomm Inc., San Diego, CA, Journal of
Communication, vol. 1, No. 1, Apr. 2006, pp. 38-47. cited by
applicant .
W. Hu et al., Efficient, Flexible, and Scalable Inter-Network
Spectrum Sharing and Communications in Cognitive IEEE 802.22
Networks, Feb. 14, 2008, pp. 1-9, Los Angeles, CA. cited by
applicant.
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Primary Examiner: Hsu; Alpus H
Attorney, Agent or Firm: Hogan Lovells US LLP
Parent Case Text
RELATED APPLICATION
The present application relates to and claims the benefit of
priority to U.S. Provisional Patent Application No. 61/158,855
filed Mar. 10, 2009, which is hereby incorporated by reference in
its entirety for all purposes as if fully set forth herein. The
present application is further related to U.S. patent application
Ser. No. 12/721,257, filed Mar. 10, 2010 entitled, "Frame-Based,
On-Demand Spectrum Contention Protocol Specifications; U.S. patent
application Ser. No. 12/721,374, filed Mar. 10, 2010 entitled,
"Frame-Based, On-Demand Spectrum Contention Methodology; U.S.
patent application Ser. No. 12/721,387, filed Mar. 10, 2010
entitled, "Frame-Based, On-Demand Spectrum Protocol Vector
Messaging; U.S. patent application Ser. No. 12/721,400, filed Mar.
10, 2010 entitled, "Frame-Based, On-Demand Spectrum Contention Data
Frame Acquisition; and U.S. patent application Ser. No. 12/721,417,
filed Mar. 10, 2010 entitled, "Frame-Based, On-Demand Spectrum
Contention Source Resolution; which are each hereby incorporated by
reference in their entirety for all purposes as if fully set forth
herein.
Claims
I claim:
1. A method of operating a cognitive radio (CR) communication
network, the method comprising: operating the (CR) communication
network using synchronized transmission frames and superframes to
provide communication services within cells of base stations of the
CR communication network; operating a communication link between
the base stations; maintaining a schedule of assignments (SchAs) of
frames, within a single channel, to the base stations, wherein each
frame is assigned to at most one base station for exclusive use for
the communication services by the base stations; communicating the
SchAs between the base stations on the communication link; and
using a frame contention among a plurality of contending base
stations to share use of the single channel by assigning individual
frames to base stations for scheduled sole use for communication
services; wherein the frame contention comprises making
assignments, in the SchAs, of individual frames of subsequent
superframes of the single channel among the plurality of contending
base stations by comparing spectrum contention numbers (SCNs) which
are randomly chosen from a finite set of numbers in which each
number is equally likely; and wherein the frame contention further
comprises destination resolution, by which a destination base
station, which has scheduled use of a set of frames in a subsequent
superframe, resolves the frame contention initiated by at least one
base station seeking to obtain the scheduled use of some or all of
the frames in the set.
2. The method according to claim 1, wherein the frame contention is
initiated by the at least one base station transmitting either of a
source request message (SC REQ) or a source acknowledgement message
(SC ACK), wherein each of SC REQ and SC ACK includes a source SCN
generated at each of the at least one base station.
3. The method according to claim 2, wherein destination resolution
further comprises the destination base station generating a
destination SCN comparing each received source SCN with the
destination SCN, and assigning scheduled use of the contended for
frame or frames among the plurality of contending base stations on
the basis of the comparison.
4. The method according to claim 3, wherein responsive to at least
one base station other than the destination base station being
assigned at least one of the frames of the set, further comprising
the destination base station transmitting a release acknowledgement
message comprising information of the frame or frames to be
reassigned and the base station or base stations to which the frame
or frames are reassigned.
5. The method according to claim 4, wherein the reassignment is for
a frame or frames in the superframe immediately following the
superframe during which the frame contention occurs.
6. The method according to claim 3, wherein responsive to the
destination base station retaining the scheduled use of all the
contended for data frame or frames as a result of the frame
contention, the destination base station transmitting a response
message comprising information that the contended for frame or
frames are not reassigned.
7. The method of claim 3, wherein a base station initiates the
frame contention only if the base station determines that the need
for communication services within its cell exceeds the
communication services available in unscheduled frames of
subsequent superframes.
8. The method of claim 3, wherein the SCNs are chosen independently
at each of the at least one base station initiating the frame
contention, and at the destination base station.
9. The method of claim 1, wherein the finite set of numbers from
which SCNs are chosen is a set of integers {0, 1, . . . ,
2.sup.X-1}, where X is a number of binary digits in a fixed point
integer used by the CR communication network.
10. The method of claim 1, wherein there are 16 frames in each
superframe.
11. The method of claim 1, wherein the communication link between
base stations is accomplished through use of beacon windows at the
end of each frame.
12. The method of claim 1 further comprising, simultaneously for a
plurality of channels of the CR communication network, maintaining
a SchAs of frames to base stations, and using the frame contention
and destination resolution to share use of one or more of the
plurality of channels.
13. A system for a cognitive radio (CR) communication network, the
system comprising: a plurality of base stations able to exchange
messages on a communication link, and using synchronized frames and
superframes for communication services within each base station's
cell, wherein the system maintains a schedule of assignments
(SchAs) of frames within a channel to the base stations, wherein
each frame is assigned to at most one base station for exclusive
use for communication services by the base station, wherein the
system communicates the SchAs between the base stations on the
communication link; wherein the system operates a frame contention
among a plurality of contending base stations to share use of a
single channel by assigning frames to base stations for scheduled
exclusive use for communication services; wherein the frame
contention comprises assigning individual frames of subsequent
superframes of the single channel among the plurality of contending
base stations by comparing spectrum contention numbers (SCNs) which
are randomly chosen from a finite set of numbers in which each
number is equally likely; and wherein the frame contention
comprises destination resolution by which a destination base
station, which has scheduled use of a set of frames in a subsequent
superframe, resolves the frame contention initiated by at least one
other source base station, each of the at least one other source
base station seeking to obtain the scheduled use of some or all of
the frames in the set, with said initiation comprising the sending
of a request message by each of the at least one other source base
stations.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of the present invention relate, in general, to
cognitive radio networks and more particularly to on-demand
spectrum contention protocol specifications.
2. Relevant Background
Modern society is increasingly dependent on the radio spectrum. The
rapid increase in wireless services and devices such as mobile
communications, public safety, Wi-Fi, and informational broadcast
serve as indisputable examples of how society uses the radio
spectrum on a day-to-day basis. Unlicensed transmission bands can
play a key role in the wireless ecosystem. Specifically Television
("TV") bands are significantly underutilized.
Cognitive Radio ("CR") is an enabling technology that allows
unlicensed radio transmitters to operate in the licensed bands at
locations when that spectrum is temporarily not in use. Based on
cognitive radio technology the Institute of Electrical and
Electronics Engineers ("IEEE"), following a Federal Communication
Commission ("FCC") Notice of Proposed Rulemaking in 2004, has
fostered 802.22 as an emerging standard for Wireless Regional Area
Networks ("WRAN") aiming to provide alternative broadband wireless
access in, among other places, rural areas. CR operates on a
license-exempt and non-interference basis in the TV band (between
47-910 MHz) without creating harmful interference to the licensed
services, which include, among others, Digital TV ("DTV") and Part
74 devices (e.g. wireless microphones).
In a typical deployment scenario, multiple WRAN cells, each of
which comprises a base station ("BS") and associated customer
premise equipments ("CPE"), may operate in the same vicinity while
coexisting with DTV and Part 74 devices. In order to effectively
avoid harmful interference to these licensed incumbents, the set of
channels on which the WRAN cells are allowed to operate could be
quite limited. For example as shown in FIG. 1, residing within the
protection contours of DTV 140 and wireless microphones 150, both
Network 1 110 and Network 3 130 are only allowed to operate on
channel A, while Network 2 1220 may occupy either channel A or B,
assuming that in total only 3 channels (channels A, B and C) are
available. If WRAN1 and WRAN3 (also referred to herein as Network 1
and Network 2) attempt to perform data transmissions on channel A
simultaneously, mutual interference between these collocated WRAN
cells could degrade the system performance significantly.
The coexistence (sharing of resources) between incumbent users and
secondary users is referred to as incumbent coexistence, and the
coexistence between WRAN cells is referred to as self-coexistence.
There are two main objectives in self-coexistence: minimizing the
self-interference between co-channel overlapping cells, and
satisfying the Quality-of-Signal ("QoS") of the cells' admitted
service workloads in a dynamic spectrum excess environment.
Distributed, cooperative, and real-time spectrum resource sharing
protocol is called On-Demand Spectrum Contention ("ODSC"). The
basic mechanism of ODSC is as follows: on an on-demand basis, BSs
of the coexisting WRAN cells contend for the shared spectrum by
exchanging and comparing randomly generated spectrum access
priority numbers via Medium Access Control ("MAC") layer messaging
on an independently accessible inter-network communication channel.
The contention decisions are made by the coexisting network cells
in a distributed way. Only the winner cell, which possesses a
higher spectrum access priority compared to those of the other
contending cells (the losers), can occupy the shared spectrum.
The effectiveness of the ODSC protocol relies on the availability
of an efficient and reliable inter-network communication channel
for the interactive MAC message exchanges among network cells. In
fact, in addition to supporting cooperative spectrum sharing
protocols such as ODSC, a reliable inter-network communication
channel is also indispensable to other inter-network coordinated
functions for 802.22 WRAN and, in general, other types of cognitive
radio based networks (e.g. inter-network synchronization of quiet
periods for spectrum sensing, and coordinated frequency hopping).
Beacon-based inter-network communication protocol called Beacon
Period Framing ("BPF") protocol is another technique used to
realize a means for reliable, efficient, and scalable inter-network
communication channel sharing by reusing the Radio Frequency ("RF")
channels occupied by the network cells.
ODSC is a coexistence protocol that employs interactive MAC
messaging on the inter-network communication channel to provide
efficient, scalable, and fair inter-network spectrum sharing among
the coexisting WRAN cells. To achieve these design goals, ODSC
allows the coexisting WRAN cells to compete for the shared spectrum
by exchanging and comparing randomly generated contention access
priority numbers carried in the MAC messages. Such spectrum
contention process is iteratively driven by spectrum contention
demands (i.e. intra-cell demands for additional spectrum resources
to support data services, and inter-cell demands requesting for
spectrum acquisitions). The contention decisions are made by the
coexisting network cells in a distributed way, which allows an
arbitrary number of cells to contend for the shared spectrum in the
proximities without relying on a central arbiter. Instead of
behaving selfishly, the competing cells cooperate with one another
to achieve the goals of fair spectrum sharing and efficient
spectrum utilization.
Currently, before initiating MAC layer messaging of the ODSC
protocol, a WRAN cell that is demanding additional spectrum
resource first evaluates and selects a channel on which no
incumbent is detected. The cell then verifies whether the selected
channel can be shared, employing the transmit power control ("TPC")
technique, with all other co-channel communication systems in the
neighborhood. If it is feasible, the WRAN cell schedules its data
transmissions on the selected channels with appropriate TPC
settings. Otherwise, ODSC messaging takes place allowing
cooperative spectrum contention among WRAN cells to share the
target channel in a time-sharing manner.
As can be appreciated by one skilled in the relevant art,
overlapping (one-hop) cells must compete for the use of the same
spectrum in order to minimize or eliminate mutual interference that
may render both cells unreliable. As described in commonly assigned
U.S. patent application Ser. No. 12/354,606 entitled, "On-Demand
Spectrum Contention for Inter-Cell Spectrum Sharing in Cognitive
Radio Networks", upon capturing the use of a particular channel,
the occupying WRAN cell, referred to as the ODSC destination
("DST"), announces the occupancy to other cells within one-hop
using an ODSC announcement message ("ODSC_ANN"). Other
spectrum-demanding WRAN cells, referred to individually as ODSC
source ("SRC"), receives the ODSC announcement messages that are
regularly broadcasted by the DST cells. If a SRC receives ODSC_ANN
messages from multiple DSTs, it randomly selects one of the DSTs.
Thereafter the SRC decodes the message from the selected DST and
then sends an ODSC request message ("ODSC_REQ") that it is seeking
access to the channel occupied by the selected DST. The request
message includes a spectrum access priority number ("SAPN"), which
is either a floating point number uniformly selected from [0, 1] or
a fixed point number uniformly selected from [0, 2.sup.x-1]
(wherein x is the number of binary bits representing the fixed
point number). Each DST maintains an ODSC_REQ window so as to allow
multiple SRCs to submit ODSC_REQ messages at different time
instances without losing its own fair chance to participate in the
contention process. At the end of an ODSC_REQ window, if any
ODSC_REQs are received, the DST randomly generates its own SAPN and
compares it with the smallest SAPN carried in the received ODSC_REQ
messages. When the DST's SAPN is smaller (i.e. possesses higher
priority), DST sends each SRC an ODSC response message ("ODSC_RSP")
indicating a contention failure. Otherwise, the SRC with the
smallest SAPN will receive an ODSC_RSP with an indication of
contention success meaning that access and control of the spectrum
resource (channel) will be relinquished by the DST in favor of the
winning SRC. The DST also sends a message to the other SRCs
informing the SRCs of a contention failure. As one skilled in the
art will recognize other criteria may be used to determine SAPN
priority. For example, the contention participant possessing the
largest SAPN may win the contention in another embodiment of the
invention.
Upon receiving a success notice, the winner SRC broadcasts an ODSC
acknowledgement ("ODSC_ACK") indicating the time, Tacq, at which it
intends to acquire the channel from the selected DST. All DSTs that
are on the same channel as the one being contended for and are
within a one-hop distance of the winner SRC respond to the ODSC_ACK
by scheduling a channel release to occur at Tacq and broadcast an
ODSC release message ("ODSC_REL") to the neighborhood. The ODSC_REL
contains information about the channel to release, the channel
release time (set to Tacq), and the identification of the winner
SRC that will acquire the channel. If the ODSC_ACKs are received
from multiple SRCs before the channel is released, a DST selects
the earliest Tacq specified in the received ODSC_ACK as the channel
release time. This avoids collisions between the neighboring DST
and SRC when the channel switching times do not agree. All SRCs
that capture the ODSC_REL will also schedule channel acquisitions
at Tacq as long as it is determined from the ODSC_REL that the
one-hop DST is releasing the channel to either itself or to a
winner SRC that is multiple hops away. On the other hand, if
multiple ODSC_RELs with different Tacq are received before the
channel switching, the earliest Tacq is taken for channel
acquisition.
In a large scale network, it is likely that multiple DSTs and
multiple SRCs coexist. As the contention processes are fully random
and independent, different SRCs could select their own DSTs to
contend for the same spectrum resource and the contention outcomes
(i.e. winners of the contention and channel acquisition/release
times) could be in conflict. The ODSC message flow described above
is designed to coordinate the discrepancies between the conflicting
contention decisions in order to ensure the stability of the
coexistence behaviors and avoid loss of spectrum efficiency across
the networks. However, at any one time only one network cell can
utilize the shared channel in close proximity. While the network
cell occupying the channel sends and receives data over a
particular period of time, other neighboring network cells remain
idle. This is true even when the network cell occupying the channel
may not be fully utilizing the bandwidth of the channel over its
allocated period of time. Additionally a network cell demanding a
spectrum resource would have to remain idle for a relatively long
duration (in the order of plurality of frames) until the channel to
share is released by the occupying network cell. As a consequence,
such a potentially long turnaround time of channel acquisition may
negatively impact the quality of service ("QoS") of time sensitive
applications due to the long service interruptions. Spectrum
sharing on a finer granularity than a channel (such as frame-based)
is advantageous to enhance both the utilization of the operating
spectrum and the QoS of the application.
What is needed is a set of general mechanisms for an arbitrary
number of distributed network devices to share limited spectrum
resources. Although the above description of the ODSC protocol
outlines how a protocol is employed for resolving problems of radio
resource sharing where the basic unit of the spectrum resource is a
radio frequency channel, the same principal of ODSC applicability,
without loss of generality, is desirable to other, more fine
grained, apportionment of the shared spectrum. It is desirable to
apportion the shared radio spectrum so that any effective
combination of radio spectrum resource in both the time and
frequency domain, such as a frame on a frequency channel or
multiple frames on multiple frequency channels, can be effectively
shared.
The present invention addresses a mechanism and special features of
the ODSC protocol of spectrum sharing on a frame-by-frame basis.
This protocol is referred to hereafter as frame-based, on-demand
spectrum contention. These and other improvements to the prior art
are addressed by one or more features of the present invention.
SUMMARY OF THE INVENTION
A frame-based, on-demand spectrum contention protocol provides fine
grained allocation of a limited spectrum resource. In a CR system,
determination of spectrum resource allocation is accomplished on a
frame-by-frame basis over a predetermined interval of frames.
According to one embodiment, a superframe comprising 16 data frames
can be apportioned for use among a plurality of overlapping network
cells such as WRAN cells so as to better and more equitably
distribute a shared spectrum resource.
For a predetermined period of time, a WRAN cell, occupying one or
more data frames of a superframe, senses whether other WRAN cells
within one hop are seeking access to same occupied frames. Likewise
a WRAN cell seeking additional spectrum resources can examine the
CR network topology to determine to which WRAN cell a request for
additional resources should be sent.
After a WRAN cell occupying a particular frame (the target frame)
receives one or more external demands for access to the target
frame of a superframe (the occupying cell can also vie to maintain
control of the target frame), a contention is declared. (Note: in
the operating environment, the WRAN cell does not possess any
preferential right to a target frame) A WRAN cell initiating access
demand and sending a contention request for the target frame is
called a contention source. The WRAN cell currently occupying the
target frame and receiving the contention request(s) from one or
more contention source is called a contention destination. Each
request includes a spectrum contention number generated, according
to one embodiment of the present invention, based on a random
process. Upon receiving the requests and the spectrum contention
number from a neighboring contention source, the contention
destination cell currently occupying the targeted frame generates
its own spectrum contention number and compares all of the
generated spectrum contention numbers (including numbers generated
by the destination cell and those numbers received from a
contention source) to determine a winner.
According to one embodiment of the present invention, the smallest
spectrum contention number of the cells vying for access to the
shared spectrum resource will win the contention. A winner is
declared and an announcement is broadcast to all cells within one
hop of the contention destination of the targeted frame, indicating
the winner of the targeted frame. The winning cell will, at the end
of a certain period, (normally the superframe) thereafter occupy
the targeted frame. Upon receiving the broadcast message announcing
the winner, the winning cell, if different than the current
occupier of the targeted frame, broadcasts to all of its one hop
neighbors of impending occupancy of a targeted frame. Thus,
networks cells that may not be within one hop of the releasing cell
will nonetheless be notified of the impending occupancy of a
targeted frame by the winning cell.
According to one embodiment of the present invention, communication
of control messages for frame-based, on-demand spectrum contention
(for example frame occupancy requests) are wirelessly conveyed
during a beacon frame window attached to the trailing edge of each
data frame. Over the span of a 16 frame superframe, 16 beacon frame
windows are available to provide information throughout the CR
network of frame allocation. For example, frames 1 though 4 can be
used for sensing contention requests. The contention resolution can
occur during frames 5 and 6 with a response broadcast on frame 7.
Acknowledgements by the winning frames can be broadcast on frame 8
with a release of the frame broadcast on frame 16.
Other informational communication schemes operable to convey
synchronization and frame allocation data amongst a plurality of
cells are equally applicable to the various embodiments of the
present invention as are the factors used to determine which cell
in the contention process will gain access to the contended
spectrum resource.
The features and advantages described in this disclosure and in the
following detailed description are not all-inclusive. Many
additional features and advantages will be apparent to one of
ordinary skill in the relevant art in view of the drawings,
specification, and claims hereof. Moreover, it should be noted that
the language used in the specification has been principally
selected for readability and instructional purposes and may not
have been selected to delineate or circumscribe the inventive
subject matter; reference to the claims is necessary to determine
such inventive subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned and other features and objects of the present
invention and the manner of attaining them will become more
apparent, and the invention itself will be best understood, by
reference to the following description of one or more embodiments
taken in conjunction with the accompanying drawings, wherein:
FIG. 1 shows an exemplary overlapping network configuration of a TV
wireless system employing cognitive radios as would be known to one
of reasonable skill in the relevant art;
FIG. 2 is a high level block diagram depiction of a superframe
structure utilized in a frame-based, on-demand spectrum contention
protocol according to one embodiment of the present invention;
FIG. 3 is a top level flowchart for an inter-WRAM coexistence
procedure employing frame-based, on-demand spectrum contention
protocols according to one embodiment of the present invention;
FIG. 4 is a graphical depiction of a typical message flow carried
out via beacon windows of the frame-based, on-demand spectrum
contention protocol according to one embodiment of the present
invention;
FIG. 5 shows a flowchart of an overall procedure for frame-based,
on-demand spectrum contention according to one embodiment of the
present invention;
FIG. 6 depicts a high level flowchart of one method embodiment of
the present invention for determining the availability of data
frames in an frame-based, on-demand spectrum contention
environment;
FIG. 7 is a flowchart of one embodiment of the present invention
for frame acquisition in a frame-based, on-demand spectrum
contention environment;
FIG. 8 is a flowchart of a procedure for a frame-based, on-demand
source spectrum contention (as executed by a spectrum contention
source) according to one embodiment of the present invention;
FIG. 9 is a flowchart of a procedure for a frame-based, on-demand
destination spectrum contention (as executed by a spectrum
contention destination) according to one embodiment of the present
invention;
FIG. 10 is a high level flowchart of message generation at a
spectrum contention destination involving multiple frames and
multiple spectrum contention sources, according to one embodiment
of the present invention;
FIG. 11 is a high level flowchart of the release of pending
operations at a contention destination, according to one embodiment
of the present invention;
FIG. 12 is a graphical depiction of three overlapping WRAN networks
and their respective communication paths used for evaluation of a
frame-based, on-demand spectrum contention protocol; and
FIG. 13 is an overlapping wireless CR network configuration of a
plurality of overlapping base stations implementing a frame-based,
on-demand spectrum contention resolution protocol according to one
embodiment of the present invention.
The Figures depict embodiments of the present invention for
purposes of illustration only. One skilled in the art will readily
recognize from the following discussion that alternative
embodiments of the structures and methods illustrated herein may be
employed without departing from the principles of the invention
described herein.
Glossary and Acronyms
As a convenience in describing the invention herein, the following
glossary of terms is provided. Because of the introductory and
summary nature of this glossary, these terms must also be
interpreted more precisely by the context of the Detailed
Description in which they are discussed.
Spectrum Contention Source ("SC-SRC")--the WRAN cell that is
demanding additional spectrum resources (i.e. data frames
transmission opportunities on a TV channel) and is initiating an
interactive spectrum contention process with the target Spectrum
Contention Destination.
Spectrum Contention Destination ("SC-DST")--a WRAN cell that is the
target of the spectrum contention request initiated by the SC-SRC,
and is the occupier of the spectrum resources being requested to be
shared with the SC-SRC.
Spectrum Contention Number ("SCN")--the contention number randomly
generated by SC-SRCs and SC-DSTs for determining the priority of
spectrum access.
Spectrum Contention Request ("SC-REQ")--This is a unicast request
message transmitted by the SR-SRC for initiating the spectrum
contention process.
Spectrum Contention Response ("SC-RSP")--This is a unicast response
message transmitted by the SC-DST responding to the requesting
SC-SRC with regard to the contention results.
Spectrum Contention Acknowledge ("SC-ACK")--A broadcast
acknowledgement message transmitted by the winner SC-SRC indicating
the confirmation of spectrum acquisitions.
Spectrum Contention Release ("SC-REL")--A broadcast message
transmitted by the granting SC-DST indicating the announcement of
the spectrum releases.
Target Frame--a particular frame in a superframe which is the focus
of a contention process between two or more overlapping network
cells.
DESCRIPTION OF THE INVENTION
Embodiments of the present invention are hereafter described in
detail with reference to the accompanying Figures. Although the
invention has been described and illustrated with a certain degree
of particularity, it is understood that the present disclosure has
been made only by way of example and that numerous changes in the
combination and arrangement of parts can be resorted to by those
skilled in the art without departing from the spirit and scope of
the invention.
A frame-based, on-demand spectrum contention protocol enables
dynamic spectrum sharing for coexistence operations among a
plurality of overlapping wireless network cells. As previously
described, wireless cells in a CR communication system contend for
the use of shared resources. As a means to efficiently and
effectively utilize the available communication spectrum, CR
systems initiate a competitive process where each system contends
for the use of the same resource.
As is well known to one of ordinary skill in the relevant art,
wireless communication between a base station ("BS") and one or
more Consumer Premise Equipment ("CPE") within its area of
influence is accomplished via one or more channels. As discussed,
in commonly assigned U.S. patent application Ser. No. 12/354,606,
entitled "On-Demand Spectrum Contention for Inter-Cell Spectrum
Sharing in Cognitive Radio Networks" an interactive message
exchange can be undertaken to resolve contentions for the use of a
particular channel. In such situations, using the ODSC protocol, a
plurality of base stations in coexisting (overlapping) WRAN cells
contend for the use of a particular channel of a shared spectrum.
As a result of the contention process, a single base station gains
complete access to a particular channel until another contention
for the shared spectrum is raised.
During the period of time in which the winning base station has use
of the channel, other coexisting base stations are precluded from
communicating. The present invention provides a message-based,
demand driven, distributed spectrum sharing protocol for use in
contention based CR communication systems. Rather then resolving
shared spectrum resource contentions on a coarse-grain,
channel-by-channel basis, the present invention enables a
fine-grain, frame based, resolution of shared spectrum contentions.
While the embodiments of the present invention are largely
described with regard to wireless regional area networks, one of
reasonable skill in the art will understand that the concepts
presented herein are equally applicable to any wireless network and
cognitive radio communication system.
According to one or more embodiments of the present invention,
messages are exchanged between base stations contending for a
commonly shared resource to determine their respective rights to
that resource. While the present invention is primarily described
with reference to the coexistence contention process for a shared
resource associated with a single channel, one of ordinary skill in
the relevant art will recognize that the same contention protocol
is equally applicable to contentions involving multiple frames
among multiple channels or generally a fractional combination of
channels in both the time and frequency domain. Indeed a likely
implementation of the present invention involves the resolution of
contentions from a plurality of base stations over a plurality of
shared resources associated with a plurality of channels involving
multiple frames in both the time and frequency domain. The present
invention contemplates the protocols presented herein are scalable
to any CR communication system regardless of size.
By using random spectrum contention numbers generated by each base
station, the present invention provides a fair and robust means for
shared spectrum contention resolution with low computational
overhead and high quality-of-signal results.
Unlike the traditional contention based medium access schemes such
as Aloha and Carries Sense Multiple Access ("CSMA"), ODSC protocol,
as described above, takes distinguishable approaches for resolving
channel access contention and mitigating access collision, aiming
to improve the spectrum access efficiency. Due to the lack of exact
knowledge of when the neighboring systems will transmit, a wireless
system using Aloha or CSMA protocol generally resolves the access
contention by deferring data transmission for a random period, and
in the case of collision, re-initiates the contention process by
setting a potentially much larger random period for the
transmission deferral (e.g. using the exponential random back-off
mechanism) in order to reduce the chance of reoccurring
collisions.
A better approach and according to one embodiment of the present
invention, ODSC allows a wireless system (IEEE 802.22 WRAN in the
present case) to compete for the channel access without resorting
to any transmission deferral which clearly sacrifices the spectrum
efficiency. This is because the contention resolution process is
carried out in parallel with the on-going data services. Moreover,
as the spectrum contention is resolved by comparing the spectrum
access priority numbers that are randomly selected from a very
large pool of values, the likelihood of access collision among
coexisting wireless systems using ODSC is effectively
minimized.
One facet of the present invention is its frame-by-frame contention
resolution within each channel's superframe. FIG. 2 is a graphical
depiction of a frame-based, on-demand ODSC communication system. In
the CR communication system shown in FIG. 2, three BSs as
originally depicted in FIG. 1 contend for the communication
resources available in channel A. Data conveyed on channel A is
packaged into discrete frames and superframes. In this particular
embodiment, a superframe is comprised of 16 frames. In other
implementations, the number of frames within a superframe may vary
and indeed the entire concept of a superframe with respect to its
relationship to individual data frames or packets may vary without
departing from the scope and intent of the present invention.
Each line shown in FIG. 2 represents frame allocation to a BS
defined network. Network 1 210 as shown in FIG. 1 is the top line
while Network 2 220 is the second line and Network 3 230 is the
bottom line. As shown in FIG. 1, Network 2 220 overlaps with
Network 1 210 and Network 3 230. Network 1 210 however is
independent of Network 3 230. Thus the same spectrum resources can
be used simultaneously by Network 1 210 and Network 3 230. The
contention for the available spectrum resource of channel A is
therefore between Network 2 220 and Networks 1 and 3 210, 230.
A superframe 240, 250 includes, according to one embodiment of the
present invention, 16 individual data frames 240.sub.0-15,
250.sub.0-15. Each data frame 240.sub.0-15, 250.sub.0-15 is
separated by a beacon window 260. Each data frame 240.sub.0-15,
250.sub.0-15 and each beacon window 260 are time partitioned and
fixed in size. And, as can be seen in FIG. 2, the superframes of
each network 210, 220, 230 are, in this example, synchronized. In
other embodiments of the present invention synchronization is not
required.
The beacon window 260 (also referred to herein as a beacon period
or beacon period frame) allows coexisting WRAN cells such as
Network 1 210 and Network 2 220, and Network 2 220 and Network 3
230 to exchange coexistence beacons for inter-network
communication. Other inter-network communication protocols and
systems can be used without detrimentally impacting the unique and
non-obvious features of the present invention. The ability for
contending networks to communicate resource needs and to
communicate resource management allocations is a fundamental aspect
of the present invention.
These and other implementation methodologies for inter-network
communication can be successfully utilized by the frame-based,
on-demand spectrum contention protocol. These implementation
methodologies are known within the art and the specifics of their
application within the context of the present invention will be
readily apparent to one of ordinary skill in the relevant art in
light of this specification. For example inter-cell communication
can be accomplished using a dedicated communication channel, one or
more dedicated communication frames within the superframe, back
channels, a wired interface such as Ethernet or other wired
communications systems, or any other means by which two or more
base stations can convey spectrum resource allocation information.
Moreover the timing of the communication is flexible and can be
adjusted to meet the needs of the network without detrimentally
altering the efficiency and success of the present invention.
FIG. 3 is a top level flowchart showing inter-WRAN coexistence
procedures. In the following description it will be understood that
each block of the flowchart illustrations, and combinations of
blocks in the flowchart illustrations, that follow can be
implemented by computer program instructions. These computer
program instructions may be loaded onto a computer or other
programmable apparatus to produce a machine such that the
instructions that execute on the computer or other programmable
apparatus create means for implementing the functions specified in
the flowchart block or blocks. These computer program instructions
may also be stored in a computer-readable memory that can direct a
computer or other programmable apparatus to function in a
particular manner such that the instructions stored in the
computer-readable memory produce an article of manufacture
including instruction means that implement the function specified
in the flowchart block or blocks. The computer program instructions
may also be loaded onto a computer or other programmable apparatus
to cause a series of operational steps to be performed in the
computer or on the other programmable apparatus to produce a
computer implemented process such that the instructions that
execute on the computer or other programmable apparatus provide
steps for implementing the functions specified in the flowchart
block or blocks.
Accordingly, blocks of the flowchart illustrations support
combinations of means for performing the specified functions and
combinations of steps for performing the specified functions. It
will also be understood that each block of the flowchart
illustrations, and combinations of blocks in the flowchart
illustrations, can be implemented by special purpose hardware-based
computer systems that perform the specified functions or steps, or
combinations of special purpose hardware and computer
instructions.
As a BS is powered on 310 it begins a BS Network discovery process
320. Other BS within its range of operation are identified directly
and by communicating with CPEs within its area of coverage other
overlapping network cells can be identified. During this period of
discovery, each BS identifies TV channel occupancies of neighboring
WRAN cells and self-coexistence window reservations of the
neighboring WRAN cells. Finally, individual frame reservation
patterns (as described hereafter) of each neighboring WRAN cell on
specific TV channels are determined. Based on its network
discovery, the BS undergoes an etiquette-based channel acquisition
330 which is to identify and acquire an available TV channel
without detrimentally affecting incumbent device operation and
neighboring WRAN cells. For example based on the TV channel
occupancy by incumbent devices and available channel spectrum
resources, a new BS may determine that it should operate on channel
A along with any other overlapping base stations. Thus, the new BS
may have to contend for a limited shared spectrum resource.
Upon choosing one or more channels on which to operate, a base
station attempts to acquire 340 exclusive use of that (those)
channel(s). To do so, a request is sent out by the base station to
determine whether any other base stations are currently using the
channel. When no response to the request is received, the
requesting BS issues an announcement of its use and effective
ownership of the channel. Shortly thereafter, the BS can use the
channel for normal data services 360.
A more frequent response to the base station's attempt to acquire
exclusive use of a channel is a denial indicating that another base
station or stations are currently using that spectrum for data
services. According to one embodiment of the present invention the
requesting base station enters an inter-WRAN frame-based, on-demand
spectrum contention process 350 for co-channel sharing. (explained
in detail below with reference to subsequent figures). Upon
successful resolution of that process the base station gains access
to at least a portion of the spectrum and begins normal data
services 360.
While the base station utilizes the spectrum for data services,
other demands or requests for the shared spectrum may arise. These
requests or demands may be externally or internally generated. An
external demand for inter-WRAN spectrum sharing 370 may arise from
another BS joining the network or an existing BS in the network
seeking additional spectrum resources. Another external demand may
be an increased utilization of the spectrum by the incumbent (TV)
resulting in a reduction in overall spectrum availability.
Similarly, an internal demand for spectrum acquisition 380 may
arise from a base station's realization that its allocated shared
spectrum is insufficient to meet its data services requirements.
For example, CPEs within its own cell may demand additional
spectrum resources. Thus, the BS internally issues a demand for
additional spectrum resources.
When a BS realizes that it possesses an internal demand for
additional spectrum resources 380, it again initiates an
etiquette-based channel acquisition procedure 330. The base station
hence reexamines the spectrum to determine if it can acquire
another channel. If the channel is acquired, the BS begins normal
data services 360 and thereafter determines whether it now
possesses enough of the spectrum to meet its internal needs. If an
additional (or different) channel is not acquired then it returns
to, and reinitiates an inter-WRAN frame-based spectrum contention
in hopes to gain more of the existing shared spectrum.
If an external demand for inter-WRAN spectrum sharing 370 is
received each participating BS (WRAN) again competes for a portion
of the shared resources. By continually evaluating the allocation
of shared resources, each WRAN gains an equal share of the shared
resource. FIG. 2 shows a representation of frame-based, on-demand
spectrum contention allocation. Shown are frames associated with
two superframes that are allocated among three overlapping WRAN
cells.
Referring again to FIG. 2, each superframe 240, 250 of a shared
channel comprises 16 data frames 240.sub.0-15, 250.sub.0-15. In the
first superframe 240 the first 3 data frames of channel A
240.sub.0, 240.sub.1, 240.sub.2 are being utilized by Network 1 210
and Network 3 230 without contention. Recall that Network 1 210 and
Network 3 230 do not overlap. During this time period frames 0-3,
Network 2 is unable to transmit or receive data and is thus
idle.
In the second superframe 250, Network 2 220 occupies the initial
data frame 250.sub.0 to the exclusion of Network 1 210 and Network
3 230. Thus, for frame 250.sub.0 Networks 1 210 and 3 230 are idle.
In this manner each of the three Networks 210, 220, 230 can be
provided shared access to the limited spectrum resource increasing
the overall quality-of-signal in each network.
FIG. 2 additionally depicts the presence of a beacon window 260
following each data frame 240, 250. Upon the initiation of an
inter-WRAN frame-based ODSC these beacon windows are used to carry
request, response or acknowledgement messages between the
participating WRAN cells.
FIG. 4 is a graphical depiction of a typical message flow carried
out via beacon windows of the frame-based, on-demand spectrum
contention protocol according to one embodiment of the present
invention. In the scenario shown in FIG. 4, three WRAN cells are
contending for a shared frame resource. Returning again to the
communication network shown in FIG. 2, assume that during an
initial etiquette-based channel acquisition process, Network 2 220
acquired sole use of channel A. Shortly thereafter, Network 1 210
and Network 3 230 joined the communication network with their cells
overlapping as shown. The message flow in FIG. 4 is an example of
Network 1 210 and Network 3 230 attempting to gain shared access to
the spectrum currently controlled by Network 2 220.
SC-SRC is a designation placed on those cells that serve as the
source of contention. In this case two WRAN BSs, Network 1 210 and
Network 3 230, are seeking additional spectrum resources and are
thus designated as a spectrum contention source 420 or SC-SRC.
Similarly, the WRAN cell that currently is in control of a spectrum
resource is designated as the destination to which the contention
is directed or SC-DST 410. As one of reasonable skill in the
relevant art will recognize, the title of SC-DST and SC-SRC is
solely based on which cell currently controls or seeks a particular
shared spectrum resource. As the allocation of the shared resource
changes, so too will the respective labels. And, indeed, a
particular cell can for one portion of the spectrum be a
destination, meaning it currently controls the spectrum, while at
the same time be a source for a contention request as it seeks
additional spectrum resources for data services.
Turning attention back to FIG. 4, each contention source, SC-SRC
issues separate spectrum contention requests 425 for additional
shared resources. Note that the requests for additional resources
can be issued at different times but, nonetheless, must be within a
certain window so as to be accepted for consideration. According to
one embodiment of the present invention, each SC-REQ includes a
spectrum contention number generated by the SC-SRC. As will be
described later, the spectrum contention number is a number used by
the SC-DST to determine resource allocation. Upon receipt of a
request or requests, the cell which is currently in control of the
resource, SC-DST, undergoes a spectrum contention analysis using
the gained various spectrum contention numbers.
In addition to the source cells requesting access to the shared
resource, the destination may also participate in the contention.
Thus, in the present example, three cells are competing for the
same shared resource. Recall that this contention is taking place
on a frame-by-frame basis. As the contention analysis takes place,
the destination cell maintains control and use of the shared
resource. While the entire contention process may occur over the
length of a single frame, other embodiments of the present
invention, a predetermined period of time, can be specified giving
the SC-DST a time period of known data frames. For example, assume
that a contention for a shared resource has been received and that
evaluation of the contention algorithms takes place over 3 frames.
During those 3 frames the SC-DST can prioritize data services
knowing that the allocation of the spectrum may soon be diminished.
Typically, the contention process is conducted and completed within
the time period elapsed during a superframe or, in one embodiment,
16 data frames. However, the resolution of a contention can be
arbitrarily set based on the needs of the CR communication
network.
Upon completion of the contention process, the SC-DST will
determine which network cell, in this case Network 1 210, Network 2
220 or Network 3 230 will gain (or maintain) control of the shared
resource. According to one embodiment of the present invention,
each destination cell knows of the topology of its one-hop
neighbors. Thus, in this example, Network 2 220 is aware that while
both Network 1 210 and Network 3 230 are within one hop of Network
2 220, Network 1 210 and Network 3 230 can operate autonomously.
Thus, if either Network 1 210 or Network 3 230 wins the contention,
the other cell can also use the shared resource.
As shown in FIG. 4, the destination cell, SC-DST, broadcasts a
response 430 providing the results of the inter-WRAN frame-based
spectrum contention to each of its one-hop neighbors in the form of
a SC-RSP message. Each cell receiving the message responds with a
similar broadcast acknowledgement message 440 (SC-ACK) stating
whether or not it has received access to the shared resource.
Assume in this case that Network 1 210 had won the inter-WRAN
frame-based spectrum contention. The SC-RSP message 430 broadcast
from Network 2 220 would indicate that Network 1 210 won the
contention. Included in the message, according to one embodiment of
the present invention, would be a proposed release time of the
resource. The message may also include that Network 3 230 will also
have use of the shared spectrum as Network 1 210 and Network 3 230
do not coexist.
The broadcast acknowledgement message 440 from each SC-SRC
(Networks 1 210 and 3 230) inform its one-hop neighbors of its
impending use (or non-use) of a particular shared resource. In this
case both Network 1 210 and Network 3 230 would be informing all of
their one-hop neighbors that they are about to gain control of a
particular frame-based shared resource.
Once the acknowledgement message 440 has been sent, the SC-DST
(Network 2 220) issues a release (SC-REL) 450 relinquishing control
of the shared spectrum resource. At that point Network 1 210 and
Network 3 230 change their designations from contention source, to
contention destination. Likewise, Network 2 220, with respect to
this shared spectrum resource, can issue a spectrum contention
request making it a spectrum contention source. Assuming that a
single message can take place during any one beacon window 260, the
entire contention, response, acknowledgement and release can occur
in as little as 4 frames of a superframe.
The present invention discloses a frame-based, on-demand inter-WRAN
spectrum contention protocol. The fine-grained nature of the shared
spectrum contention process can place a single WRAN acting as both
a contention source and as a contention destination within a single
superframe on any given channel. Indeed, such a contention
resolution scheme could play out for each frame within each
superframe.
In the above scenario, Network 1 210 and Network 3 230 are seen as
having identical allocations to the shared spectrum resource. One
of reasonable skill in the relevant art will recognize, however,
that the example presented herein is a simplified version of what
is undoubtedly a more complicated scenario. The above scenario
assumes that no other one-hop neighbors of Network 1 210 and
Network 3 230 that are not affiliated with Network 2 220 have been
operating on the same shared resource. For example, it is entirely
possible that while Network 1 210, the winner of the contention
with Network 2 220 and Network 3 230, may be able to gain
operational control of a shared resource, Network 3 230 may have
another coexistence network, Network 4 (not shown) that is also
operating on, and contending for, the same frame of the same
channel In that inter-WRAN frame-based spectrum contention, Network
4 may have maintained control of the shared resource such that upon
release by Network 2 220, only Network 1 210 and not Network 3 230
may be able to utilize the shared resource.
As previously described, the WRAN BS in control of a spectrum
resource determines the winner of contention over that resource. In
doing so, the base station gathers spectrum contention numbers from
each participating WRAN cell and evaluates the values based on, in
one embodiment of the present invention, a spectrum contention
algorithm.
According to one embodiment of the present invention, the spectrum
contention algorithm is of the form:
TABLE-US-00001 Spectrum Contention (N, WRAN, SCN ,Frame) 1
.times..times..times..rarw..times..function. ##EQU00001## 2 for i
.rarw. 1 to N 3 if SCN[i] = = SCN.sub.winner 4 return
WRAN.sub.winner(Frame) .rarw. WRAN[i] and SCN.sub.winner(Frame)
Where in the algorithm,
N: total number of contending WRAN cells;
WRAN: the array of IDs of the contending WRAN cells, WRAN[i] for
i.rarw.1 to N;
SCN: the array of spectrum contention numbers of the contending
WRAN cells, in which SCN[i] is the spectrum contention number of
WRAN[i] for i.rarw.1 to N;
Frame: the data frame (spectrum resource) being contended for;
(target frame)
SCN.sub.winner(Frame): the winner spectrum contention number for
accessing the Frame; and
WRAN.sub.winner(Frame): the ID of the winner WRAN cell to access
the Frame.
Each contending WRAN cell produces and sends to the destination
cell a spectrum contention number. According to one embodiment of
the present invention the spectrum contention number, SCN.sub.i,
for WRAN cell i, WRAN.sub.i, is generated, according to one
embodiment of the present invention, as:
SCN.sub.i=RANDOM(0,2.sup.X-1).
As presented above, the winning WRAN cell of a frame-based,
on-demand inter-WRAN spectrum contention is the WRAN cell
possessing the smallest spectrum contention number. One reasonably
skilled in the relevant art will recognize that other techniques
can be used to generate a spectrum contention number. Indeed, the
algorithm presented above for resolution of a spectrum contention
may vary without departing from the scope contemplated by the
present invention.
As shown above, a spectrum contention destination collects, over a
predetermined period of time, one or more spectrum contention
numbers wherein each spectrum contention number is generated and
issued to the destination cell by a WRAN source cell contending for
use of the shared spectrum. The destination cell builds from the
received spectrum contention numbers an array comprised of each
received SCN. Each SCN in the SCN array is associated with its
generating WRAN identification number. A similar array of
contending WRAN cells is fabricated and comprised of the WRAN
identification numbers.
According to one embodiment of the present invention, the
determination of a minimum SCN necessarily identifies a WRAN cell
associated with that minimum SCN. Thus, for a particular shared
resource frame, a winning WRAN cell, WRAN.sub.winner, is
determined. Thereafter, the winning WRAN cell ID along with the
winning SCN is broadcast from the WRAN cell conducting the
contention.
FIG. 5 shows a flowchart of a frame-based, on-demand spectrum
contention protocol according to one embodiment of the present
invention. Upon initiation 505 of a contention, (block 350 of FIG.
3) the destination or deciding WRAN cell determines whether the
contention is based on an internal or external demand for
additional access to the shared spectrum resource.
Recall that an external demand 510 for acquiring access to the
occupied frames may be the result of a new or existing base station
seeking more data service bandwidth. Upon determining that an
external inter-WRAN demand for acquiring access to the occupied
frames 510 exists, the destination WRAN cell initiates a contention
520 for the targeted data frames while still behaving as a spectrum
contention destination (explained in detail with reference to FIG.
9). As the spectrum contention destination, the WRAN cell is in
control of the evaluation process of the spectrum contention
numbers, although the process itself is equitable and gives the
destination cell no inherent advantages.
When a determination is made that an internal intra-WRAN demand 530
for additional frames occurs, the destination WRAN cells first
identify 540 available (non-occupied) frames in the superframe
structure. This is done with reference to a superframe MAP. The
superframe MAP identifies frame allocation within a superframe of a
particular channel for a specific one hop WRAN neighborhood. Recall
that an internal demand occurs when a destination or controlling
WRAN cell experiences an increased need for data band width due to
internal alterations such as more usage by or presence of CPEs
within its area of coverage. Since the increased demand is
internal, it is likely that the current state of shared spectrum
allocation is not challenged by the other participating WRAN cells.
Thus, it may be possible to reallocate resources without having to
enter a full contention procedure as a contention may result in a
decrease of the destination's current resource allocation.
Once available data frames are identified 540, a course of action
is undertaken to acquire 550 one or more of the non-occupied data
frames so as to meet the increased internal demand (explained in
detail with reference to FIG. 6). Upon acquisition of the new data
frames, a query is made 560 whether additional data frames are
needed to meet the internal intra-WRAN spectrum demand.
If no additional frames are needed, the process ends 595 (returning
to block 360 of FIG. 3). Note that when a destination WRAN cell
experiences an internal demand and the superframe structure
includes non-occupied or non-used data frames, a contention for
shared spectrum resources is not necessary.
When the acquisition of non-occupied frames fails 560 to meet the
increased internal need, the destination WRAN cell selects 570
target data frames from the occupied data frames in the superframe
MAP. Once selected, the WRAN cell seeking additional data frames
based on an internal intra-WRAN spectrum demand initiates a
contention 580 (explained in detail with reference to FIG. 8). The
contention 580 is for the targeted frames and does not involve the
frames which it currently occupies. Thus, the cell seeking a
contention to resolve its internal intra-WRAN spectrum demand
assumes the role of a spectrum contention source, SC-SRC. To the
other WRAN cells using the shared spectrum resources, an external
demand 510 for their data frames has just occurred.
Upon receiving the spectrum contention request the cell(s)
occupying the targeted frames conduct a contention as previously
described. As will be understood by one of reasonable skill in the
relevant art, the result of the contention is unpredictable. It is
possible that the cell experiencing the internal intra-WRAN
spectrum demand may win the contention, gaining access to new data
frames thus resolving its internal demand. However, the losing WRAN
cell may then experience an internal demand for additional data
frames. The losing cell now enters the flowchart shown in FIG. 5 to
resolve its demand by determining whether the demand is internal
530 or external 510. The contention may also result in the WRAN
cell seeking the additional cells losing the contention. In such a
case, no additional resources have been gained from the contention
which will likely spark the need for an additional contention.
In conjunction with the acquisition of the additional data frames
from either an externally or internally generated demand, a WRAN
cell needs to determine the availability of data frames within the
superframe structure in which it is operating. FIG. 6 represents a
high level flowchart of one method embodiment of the present
invention for determining the availability of data frames in an
on-demand shared spectrum environment.
Determining frame availability begins 605 with marking 610 all of
the known available (non-occupied) frames within a superframe
structure as winner frames. With the frames identified as winner
frames, a WRAN cell seeking additional data frames can initiate
acquisition of the winning designated frames should no other claim
of ownership exist. Thus, the procedure's next task is to determine
whether another WRAN cell has gained access and control of a
particular data frame. Recall that each WRAN cell possesses a
sensing or listening (quiet) period in which it gathers information
broadcasted from other base stations. It is during this period of
the beacon window 260 in which a WRAN cell looking to gain
additional frames would find out if another nearby WRAN cell has
gained ownership of a particular data frame. Upon time out 615 of
that sensing period, a WRAN cell which has designated a frame as a
winning frame can initiate acquisition procedures. Said another
way, since no other WRAN cell has indicated that is has a
controlling interest in a particular frame, it is free to acquire
the data frame for its own use.
However, it is possible that during this sensing period the WRAN
cell may receive 630 a spectrum contention release message, SC-REL.
Such a message would indicate that a particular frame, F.sub.x, has
been released to WRAN N where N is the WRAN identification number.
Just as previously discussed in reference to FIGS. 1 and 3, it is
possible that the WRAN N and the WRAN cells seeking additional data
frames are not within one-hop of each other. Thus, upon receiving
such a SC-REL message, the WRAN cell determines 640 whether WRAN N
is a one-hop neighbor. When WRAN N is not a one-hop neighbor, then
the release of a particular frame to WRAN N does not preclude the
WRAN cells seeking additional data frames from seeking their
acquisition. In such a case a query is made to determine whether
F.sub.x is on the list of available frames. If it is, the list of
available frames is updated 670 (in this case confirming no change)
and all available frames are again marked as being winning frames
610.
When the query determines that F.sub.x is not on the list of
available frames, F.sub.x is added 665 to the list and the list is
updated 670. This iterative inquiry operates until a robust list of
available frames is determined, all of which are marked as winner
frames 610.
When the inquiry of whether WRAN N is a one hop neighbor 640 is
affirmative, an additional inquiry is made with respect to the
status of F.sub.X and its existence on the list of available frames
645. If F.sub.X is not on the list of available frames no change is
necessary as F.sub.X is not available. However, if F.sub.X is on
the list of available frames it is accordingly removed 650. Since
WRAN N is a one hop neighbor and a REL message has been issued
indicating F.sub.X has been released to WRAN N, it cannot also be
occupied by another one hop WRAN cell.
With the list of available frames constructed and each available
frame marked as a winner frame 610, the inquiry once again turns to
see if a source contention frame release message is received. When
no such message is received during a sensing period 615, a spectrum
contention number N.sub.C is generated 620 and the frame
acquisition procedure 625 (explained in detail with reference to
FIG. 7) is initiated 695 (returning the process to block 560).
FIG. 7 is a flowchart of one embodiment of the present invention
for frame acquisition in a frame-based, on-demand spectrum
contention environment. The flowchart depicted in FIG. 7 begins 705
upon initiation of the frame acquisition procedure introduced in
FIG. 6 625 and FIG. 8 890. With a list of available frames in hand,
the WRAN cell seeking additional data frames, WRAN.sub.C,
broadcasts 710 a message, SC-ACK, containing a spectrum contention
number N.sub.c announcing its intent to acquire the winner frames
beginning upon commencement of the next superframe.
In response to broadcasting such an acknowledgement message one of
three scenarios can occur. First, no other messages are received
during the sensing period meaning that no contention for the
winning frames will occur. Second, the broadcasting WRAN cell,
WRAN.sub.C, can receive a release message having another spectrum
contention number indicating that another WRAN cell, WRAN.sub.K,
has been granted access to, and control of, the same frame. And
third, another acknowledgement message can be received from another
WRAN cell, WRAN.sub.M, announcing that it too is attempting to
acquire the same data frame. Each of these scenarios is described
below in detail.
If, during the sensing period, the broadcasting WRAN.sub.C cell
receives another spectrum contention acknowledgement message,
SC-ACK 720 from WRAN.sub.X, the cells must determine which cell has
priority to the data frame. Recall that for another WRAN cell to
issue an acknowledgement message in an attempt to acquire a data
frame it has similarly determined a list of available frames. Thus,
this type of acknowledgment message is from a one-hop neighbor.
Just as original SC-ACK message includes a spectrum contention
number N.sub.C, so too does the acknowledgement message from
WRAN.sub.M, N.sub.X. To determine which WRAN cell will acquire the
available data frame, a comparison 750 of the spectrum contention
numbers takes place. If N.sub.C is smaller than N.sub.X, WRAN.sub.C
wins the contention and thereafter issues a broadcast message in
the next beacon window 260 acknowledging its intent to acquire a
winning frame at the beginning of the next superframe.
The losing WRAN, in this case WRAN.sub.M, removes its intent to
acquire the frame and is silent during the next beacon window 260.
Likewise, if WRAN.sub.C lost the contention, it would no longer
pursue that frame (marking it as a loser frame 755) and upon
arrival of the next beacon window 260, it would remain silent and
likely receive an acknowledgement message from WRAN.sub.M of its
success in acquiring that frame.
One possible outcome of WRAN.sub.C's broadcast of its intention to
acquire the winning frame(s) from the available frame listing is
the receipt of a spectrum contention release message 730, SC-REL,
from a spectrum contention destination, SC-DST. Recall that after a
contention, a destination WRAN issues a release message indicating
which WRAN cell is gaining control of a particular sheared spectrum
resource. In this case, WRAN.sub.C after issuing its broadcast
acknowledgement message of intent to acquire one or more available
frames in a particular superframe structure, may receive a spectrum
contention release, SC-REL, indicating that WRAN.sub.K has been
granted the right to acquire the same frame as is being sought
after by WRAN.sub.C. Included in the SC-REL message is the spectrum
contention number, N.sub.X, generated by WRAN.sub.K. (note:
WRAN.sub.M and WRAN.sub.K can be the same WRAN)
Recall that the destination cell releasing a shared spectrum
resource, a frame, is a one-hop neighbor of WRAN.sub.C. However,
the cell to which the spectrum contention destination is releasing
the frame may or may not be a one-hop neighbor of WRAN.sub.C. And,
if the cell gaining control of the sought after frame is not a
one-hop neighbor, the frame from WRAN.sub.C's perspective, is still
available for use.
Accordingly, the next step in one embodiment of the procedure for
frame acquisition, as shown in FIG. 7, is to determine if
WRAN.sub.K is a one-hop neighbor of WRAN.sub.C 740. When it is
determined that WRAN.sub.C and WRAN.sub.K are not one-hop
neighbors, another message is broadcast, this time without likely
receipt of a SC-REL message indicating that another WRAN has been
granted control of the same frame.
When the inquiry 740 determines that WRAN.sub.C and WRAN.sub.K are
one-hop neighbors, a comparison of each cell's spectrum contention
number is warranted. N.sub.C and N.sub.X are compared 750, in one
embodiment of the present invention, with the smaller spectrum
contention number winning. When the result is such that N.sub.C is
smaller than N.sub.X, the process recognizes a victory and another
acknowledgement message is broadcast. And, when it turns out that
N.sub.X is smaller than N.sub.C, WRAN.sub.C accepts the failure and
can consider whether the initiation of another contention at a
later time is warranted. One of reasonable skill in the art will
understand that N.sub.X of WRAN.sub.M is distinct from N.sub.X of
WRAN.sub.K.
FIG. 7 shows that the last option, post issuing a broadcast
acknowledgment message announcing intent to acquire a particular
shared spectrum resource, is silence. It is possible that after the
SC-ACK message is issued, no other acknowledgments, SC-ACK, or
other releases, SC-REL, are received. Upon expiration of a
predetermined time out period 760 the WRAN seeking control of a
particular winning frame, in this example WRAN.sub.C, can mark the
winning frame(s) as occupied 770. Once marked, the frames are
occupied in the upcoming superframe for data transport and remain
occupied until a new contention is received 795. The superframe MAP
is modified and announced accordingly.
According to one or more embodiments of the present invention, a
spectrum resource contention is a dispute over the control of a
shared spectrum resource. While a spectrum resource can be
expansively defined, it can, in one embodiment of the present
invention, comprise one or more data frames. The resolution of a
dispute as to which WRAN cell will control and occupy a particular
data frame or similar shared spectrum resource is fundamental to a
frame-based, on-demand spectrum contention protocol.
An exemplary depiction of a shared spectrum contention from the
spectrum contention source's perspective is depicted in the
flowchart of FIG. 8. According to one embodiment of the present
invention, a contention begins 805 with identifying 810 the
occupiers of targeted frames. (reference block 580 of FIG. 5) By
definition the WRAN cell that occupies a frame (shared spectrum
resource) is a spectrum contention destination. The "destination"
designation is derived from its role as the destination of one or
more contention requests for access to the frame which is under its
control.
Once a WRAN cell, WRAN.sub.C, has identified which of its neighbors
is/are occupying a sought after data frame(s) a spectrum contention
number, N.sub.C, is generated 820. A separate spectrum contention
number is generated for each destination in which a contention is
contemplated. In other embodiments of the present invention, a
spectrum contention number NC could be generated for each frame
under contention. By generating a spectrum contention number for
each destination, the conveyance of information necessary to
conduct the contention is minimized.
With a spectrum contention number in hand, the WRAN cell, acting as
a source of a contention, SC-SRC, issues a spectrum contention
request 830, SC-REQ, message to each of the targeted destination(s)
with targeted frames occupied by that destination marked in the
vector. Included in the SC-REQ is the newly generated spectrum
contention number, N.sub.C. As previously discussed, the resolution
of a spectrum contention occurs at the destination WRAN.
Consequently, once the SC-REQ has been issued, the issuing WRAN, in
this example WRAN.sub.C, waits until a response message, SC-RSP, is
received 840 from each of the destinations to which a SC-REQ has
been directed (reference FIG. 9). Note that while this and other
examples herein are described in singular context, a request for
additional data frames and a subsequent contention procedure can
occur for multiple frames within the same superframe and among
multiple channels, simultaneously. Indeed a WRAN may easily occupy
multiple roles of being both a spectrum contention destination and
source with respect to different frames on the same or different
channels at the same time.
A spectrum contention continues upon receipt of a response message
from a destination WRAN cell 850. The SC-RSP will provide the
source of the contention request with the results of the
contention. If the requesting WRAN cell, the SC-SRC, possesses a
winning spectrum contention number, then the response will indicate
that it has won the contention. Alternatively, if the requesting
WRAN cell's spectrum contention number was insufficient to secure a
victory, the response message will indicate that another WRAN cell,
possibly the destination WRAN cell, is the victor.
Upon receipt of the response message the frames in which victory
was secured are marked 860 as winner frames. Thus, consider a
situation in which a requesting WRAN is seeking access to three
data frames all controlled by another one-hop neighbor WRAN cell.
The three frames, having been identified as being occupied, are the
focus of a spectrum contention request which includes, in one
embodiment of the present invention, a unique spectrum contention
number for each frame. Upon receiving the request, the destination
conducts a comparison of the received spectrum contention numbers
and its internally generated spectrum contention numbers (assuming
that the destination cell desires to remain in control of the
frames under contention) as well as any other contention numbers
for other participating cells. It is possible that of the three
data frames sought by the source WRAN cell, only one or two of the
contentions will be successful. In these successful cases, the
targeted frames are marked 860 as being winner frames. The denied
frame(s) are accordingly marked as loser frames 870.
Once the frames are marked, another sensing period is undertaken to
determine whether additional response messages have been issued
840. At the end of a predetermined period of time, a time out
period for frame acquisition 880, the WRAN cell moves to acquire
890 control and access to the winner data frames (explained in
detail with reference to FIG. 7). Upon acquisition, and thus use
for data transfer, the contention process ends 895 (returning the
process to 595 of FIG. 5 and thus 360 of FIG. 3).
FIG. 9 is a flowchart of a procedure for a destination based
frame-based, on-demand spectrum contention according to one
embodiment of the present invention (reference block 520 of FIG.
5). Resolution of a contention takes place at the WRAN cell which
currently controls and occupies the targeted shared spectrum
resources. As discussed, such a cell is designated as the
destination of the contention.
From a spectrum contention destination cell's perspective, a
contention begins 905 with either the receipt of a spectrum
contention request 910 or a spectrum contention acknowledgement
960.
Upon receiving 910 one or more spectrum contention request messages
during a spectrum contention window from one or more spectrum
contention source WRAN cells, the messages are decoded 915 to
identify individual WRAN cells and their respective spectrum
contention numbers. Having in its possession the spectrum
contention numbers from other source spectrum contention cells, the
spectrum contention destination generates its own spectrum
contention number, N.sub.C 920.
As previously discussed a contention may involve more than one
frame within the superframe structure. According to one embodiment
of the present invention, the spectrum contention destination
process selects 925 an occupied frame, F.sub.C, that is being
contended for by one or more source cells. (Note that the multiple
frames F.sub.C can be occupied by the same destination WRAN) As
previously described, each spectrum contention request includes its
own spectrum contention number associated with each WRAN cell. In
one embodiment of the present invention a WRAN cell SRC seeking two
targeted frames, F.sub.1 and F.sub.2, would only issue on NC. In
another embodiment of the present invention, a spectrum contention
number can be associated with each frame F.sub.C. The comparison
930 is thereafter conducted for the targeted frames, F.sub.C,
between the spectrum contention number, N.sub.C, of the spectrum
contention destination and the spectrum contention numbers,
N.sub.X, of the source cells.
When the spectrum contention number, N.sub.C, is smaller than all
spectrum contention numbers, N.sub.X, carried in all the spectrum
contention request messages for the contended frame, F.sub.C, a
contention success (the destination's perspective) for those
particular data frames is declared 945. When a success is declared
for the destination, a SC_RSP message is constructed using a frame
vector issued to each SC_SRC indicating that F.sub.C is not
granted. And, alternatively, when the spectrum contention number,
N.sub.C, is larger than all spectrum contention numbers, N.sub.X,
carried in the spectrum contention request messages for the
contended frame, F.sub.C, a failure is declared 935 (reference
block 1005 of FIG. 10). Frames in which a spectrum contention
failure has been declared are marked as "to-be-released" once an
acknowledgment has been received from the winning WRAN (see
below).
A comparison of the spectrum contention numbers, N.sub.X, received
from each spectrum contention request, SC-REQ, and the spectrum
contention number, N.sub.C, generated by the spectrum contention
destination, is conducted for each occupied frame that is in
contention 940. Upon the resolution of contention for each occupied
frame identified by the received spectrum contention request
messages, a release is pending 950 (reference block 1105 of FIG.
11). For the frames in which a contention failure has been
identified the release message would indicate that the winning
spectrum contention source has gained control of the designated
frame. And, in the situation wherein the spectrum contention
destination was victorious in the contention, the release message
would indicate that control of the applicable frame would remain
with the spectrum contention destination. With the release pending
950 a release message is generated 955 containing the winning
spectrum contention number announcing to the winning WRAN cell that
F.sub.C is released at the start of the next superframe.
The other possible initiation of a shared spectrum contention is
upon receipt 960 of a spectrum contention acknowledgment message,
SC-ACK, containing a spectrum contention number, N.sub.X, from a
neighboring WRAN.sub.M cell announcing its intent to acquire a
frame which is currently occupied by the destination. For example,
with additional reference to FIG. 2, a contention process between
Network 1 210 and Network 2 220 can result in Network 2 220 issuing
an acknowledgement message to Network 3 230. It is this additional
acknowledgement message between Network 2 220 and Network 3 230
from the contention between Network 1 210 and Network 2 220 that is
the subject of SC_ACK message of FIG. 9 960. Upon receipt of such
an acknowledgment message, the frame under contention, F.sub.X, is
marked as a frame to be released 965. Recall that a spectrum
contention acknowledgment message is generated upon the
determination that a frame is available. Thus, upon receipt of a
spectrum contention acknowledgment message, no contention is
required.
Accordingly, once the frame, F.sub.X, has been marked to be
released 965, a spectrum contention release message is broadcast to
announce that the frame, F.sub.X, will be released 970 to
WRAN.sub.M starting from the next superframe.
Upon expiration of a predetermined period of time, all frames
marked as "to-be-released" starting from the next superframe are
released 980 at the beginning of the next superframe. The process
thereafter ends 995 (reference block 595 of FIG. 5). A
corresponding spectrum contention response message is constructed
by the destination using frame vectors for all spectrum contention
sources in which the contention was not successful and access to
the targeted frame was not gained.
FIG. 10 is a high level flowchart of a spectrum contention failure
for a data frame at a spectrum contention destination involving
multiple frames, according to one embodiment of the present
invention (reference block 935 of FIG. 9). Recall that a spectrum
contention destination may be in control of more than one frame of
a 16 frame superframe structure. Upon receipt of a spectrum
contention request, the above-described contention process is
undertaken to determine whether occupancy of the frame will remain
with the destination or whether the frame will be released.
Upon determination that, from the destination's perspective, the
contention for a frame has failed, a process is begun 1005 to
identify 1010 the winning spectrum contention source for each
frame. Recall that in the previous method the destination simply
determined that in comparison with the received spectrum contention
numbers, its own internally generated spectrum contention number
was insufficient to maintain control and occupancy of the targeted
spectrum resource. Thereafter, and according to one embodiment of
the present invention, a determination is made to identify 1010
which spectrum contention source for a particular frame, F.sub.C,
is associated with the winning spectrum contention number.
Once the winning spectrum contention source has been identified for
each frame F.sub.C, a spectrum contention response message is
constructed 1030 using frame vectors to the winning spectrum
contention source informing it of its victory. Likewise, for all
remaining spectrum contention sources in which the attempt to gain
access to frame F.sub.C was a failure, a spectrum contention
response message is constructed 1040 by the destination (again
using frame vectors) informing the spectrum contention sources that
the attempt to gain access to frame F.sub.C has failed.
FIG. 11 is a high level flowchart of the release of pending
operations at a contention destination, according to one embodiment
of the present invention. Upon construction of the success and
failure spectrum contention response messages, the messages are
sent 1150 to the appropriate source WRAN cells by the destination.
After the spectrum contention response, SC-RSP, message is sent,
the destination waits 1160 a predetermined period of time for a
spectrum contention acknowledgment from each source. When an
acknowledgment message, SC-ACK, is received 1170 from the winning
spectrum contention source WRAN the frame, F.sub.C, is marked as
"to-be-released" 1180. The process iteratively continues, waiting
for additional SC_ACK messages 1160, until a time out period is
obtained 1190 ending the process 1195.
As shown above, a WRAN cell, acting as a spectrum contention
destination or a spectrum contention source, can effectively and
efficiently manage, gain and release shared spectrum resources on a
frame-by-frame basis over the superframe structure. Thus, according
to one embodiment of the present invention, data frames of any
superframe of a spectrum resource can be reallocated on a
frame-by-frame basis beginning with each superframe as the needs of
the WRAN cells within a cognitive radio communication network
vary.
One of reasonable skill in the relevant art will appreciate that a
reliable and efficient inter-network communication mechanism for
coexistence is necessary for WRAN cells to effectively execute a
frame-based, on-demand spectrum contention protocol. One means by
which to establish inter-network communication is via the beacon
window following each data frame. Other communication mechanisms
are possible and may be modified to align with the teachings and
spirit of the present invention. With the synchronization of the
frame/superframe structure between inter-network WRAN cells a fine
grain spectrum sharing is achievable.
As discussed above, inter-network communication can occur,
according to one embodiment of the present invention, via spectrum
contention messaging such as request, response, acknowledgement and
release messages. The messages are transmitted in the payload of a
contention beacon period packet.
According to one embodiment of the present invention, a spectrum
contention request message, SC-REQ, can be of the following
format.
TABLE-US-00002 Syntax Size Notes SC_REQ_IE_Format( ) { Element ID 8
bits Indication of the Message Type Length 8 bits BS ID of 48 bits
The MAC address of the contention source's base Contention Source
station. BS ID of 48 bits The MAC address of the contention
destination's base Contention station. Destination Sequence number
8 bits Incremented by 1 by the source whenever any of the following
three fields change. The contention destinations shall discard the
repeated SC_REQ IEs. Spectrum 16 bits A random number to show the
priority to contend for Contention spectrum resource of the target
TV channel. Number (SCN) TV Channel 8 bits The TV channel being
requested by the contention number source Contention 16 bits A bit
vector indicating the indexes of data frames Request Frame within a
superframe that the Contention Source Index Vector WRAN requests to
acquire (through the contention) for its data services starting
from the next superframe. For each of the 16 bits as shown below,
the corresponding frame is requested for the contention when a
bit's value is set to 1. Otherwise, the bit value of the
corresponding frame is set to 0. Bit 0: Frame 0; Bit 1: Frame 1;
Bit 2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5: Frame 5; Bit
6: Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9: Frame 9; Bit 10:
Frame 10; Bit 11: Frame 11; Bit 12: Frame 12; Bit 13: Frame 13; Bit
14: Frame 14; Bit 15: Frame 15. }
A spectrum contention response message, SC-RSP, is sent to inform a
contention source whether a request for a targeted spectrum
resource (frame) was successful. As discussed herein, such a
message is transmitted from a destination WRAN after it has
received a spectrum contention request message. A spectrum
contention response message can be, according to one embodiment of
the present invention, of the following format.
TABLE-US-00003 Syntax Size Notes SC_RSP_IE_Format( ) { Element ID 8
bits Indication of the Message Type Length 8 bits BS ID of the 48
bits Copy from the corresponding CC_REQ IE received Contention
Source BS ID of the 48 bits MAC address of the Spectrum Contention
Destination BS. Contention Destination Sequence number 8 bits Copy
from the CC_REQ. TV Channel 8 bits The TV channel requested by the
Contention Source BS number Contention 16 bits A bit vector
indicating the contention results determined by the Response Frame
channel contention algorithm for the data frames within a Index
Vector superframe that the contention source WRAN requests to
acquire. These contention results will be effective starting from
the next superframe. For each of the 16 bits as shown below, the
corresponding frame is granted to the contention source when a
bit's value is set to 1. Otherwise, the frame is not granted. For a
data frame that is not requested by any contention source, the
corresponding bit is set to 0. Bit 0: Frame 0; Bit 1: Frame 1; Bit
2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5: Frame 5; Bit 6:
Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9: Frame 9; Bit 10:
Frame 10; Bit 11: Frame 11; Bit 12: Frame 12; Bit 13: Frame 13; Bit
14: Frame 14; Bit 15: Frame 15. }
The spectrum contention acknowledgement message of the present
invention is typically sent in a contention beacon period burst
payload by the contention source. It is used to notify contention
destinations that the contention source will occupy the
destination's working shared spectrum or give up a request to do
so. For example, a contention source will typically notify a
contention destination that it will occupy a shared spectrum
resource when it receives a response message with a contention
success indication from all of the contention destinations.
Otherwise, the contention source will notify the contention
destinations that it will relinquish control of the shared spectrum
resource if it receives a response message with a rejection
indication from any of the contention destinations. According to
one embodiment, the format of an acknowledgment message is the
following.
TABLE-US-00004 Syntax Size Notes SC_ACK_IE_Format( ) { Element ID 8
bits Length 8 bits Source Id 48 bits The MAC address of the
contention source Destination (Broadcast) 48 bits The MAC address
of Message Broadcast Id Sequence number 8 bits Same as the
corresponding SC_REQ IE. The contention destinations shall discard
the repeated CC_ACK IE being received TV Channel number 8 bits The
TV channel being requested by the contention source Contention 16
bits A bit vector indicating the contention results determined by
Acknowledgement the channel contention algorithm for the data
frames within Frame Index Vector a superframe that the contention
source WRAN will acquire starting from the next superframe. For
each of the 16 bits as shown below, the corresponding frame will be
occupied by the contention source when a bit's value is set to 1.
Otherwise, the frame will not be occupied. Bit 0: Frame 0; Bit 1:
Frame 1; Bit 2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5:
Frame 5; Bit 6: Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9:
Frame 9; Bit 10: Frame 10; Bit 11 Frame 11; Bit 12: Frame 12; Bit
13: Frame 13; Bit 14: Frame 14; Bit 15: Frame 15. Spectrum
Contention 16 bits The winning SCN used in SC_REQ message, showing
the Number (SCN) priority to contend for spectrum resource of the
target TV channel. BS ID of the granting SC- 48 bits The ID of the
SC-DST WRAN cell granting the access to DST the data frame that are
being acquired by the winning SC- SRC (this is used to enable
"clear to send"). }
And, similarly, a spectrum contention release message is typically
a broadcast type of message transmitted by the spectrum contention
destination which has granted access to a particular shared
spectrum resource announcing the resource's release. A typical
release message, according to one embodiment of the present
invention, can be of the following format.
TABLE-US-00005 Syntax Size Notes SC_REL_IE_Format( ) { Element ID 8
bits Length 8 bits Source Id 48 bits The MAC address of the
contention destination BS. Destination (Broadcast) 48 bits The MAC
address of Message Broadcast Id Sequence number 8 bits Same as the
corresponding CC_REQ IE. The contention destinations shall discard
the repeated SC_REL IE being received TV Channel number 8 bits The
TV channel being requested by the contention source Contention
Release 16 bits A bit vector indicating the contention results
determined by Frame Index Vector the channel contention algorithm
for the data frames within a superframe that the contention source
WRAN will acquire starting from the next superframe. For each of
the 16 bits as shown below, the corresponding frame will be
occupied by the contention source when a bit's value is set to 1.
Otherwise, the frame will not be occupied. Bit 0: Frame 0; Bit 1:
Frame 1; Bit 2: Frame 2; Bit 3: Frame 3; Bit 4: Frame 4; Bit 5:
Frame 5; Bit 6: Frame 6; Bit 7: Frame 7; Bit 8: Frame 8; Bit 9:
Frame 9; Bit 10: Frame 10; Bit 11 Frame 11; Bit 12: Frame 12; Bit
13: Frame 13; Bit 14: Frame 14; Bit 15: Frame 15. Spectrum
Contention 16 bits The winning SCN used in SC-REQ message, showing
the Number (SCN) priority to contend for spectrum resource of the
target TV channel. BS ID of the winning SC- 48 bits The ID of the
the SC-SRC WRAN cell granted the access to SRC the data frame that
are being released by the granting SC- DST (this is used to enable
efficient spectrum reuse). }
The frame-based, on-demand spectrum contention protocol of the
present invention provides an efficient, scalable, and fair
internetwork spectrum sharing system. The protocols of the present
invention provide simple contention processes using a random number
exchange. Contentions are conducted in parallel with ongoing data
transmissions. Thus, there is no interruption in data
communications. Collisions are avoided and there are no hidden node
problems. The protocols of the present invention are scalable in
that the decision-making process is distributed with no central
arbitrators needed. The process is stable providing cooperation
among the networks achieving a needed goal of fairness and
efficiency in spectrum sharing.
The frame-based, on-demand spectrum contention protocol presented
herein is also fair. By using a random number comparison and an
on-demand iterative contention process, the allocation of shared
network resources are equitably distributed. To verify the equity
of the protocols of the present invention multiple coexistence
scenarios were conducted using performance evaluation and
tools.
Using the NS2 model network simulator under IEEE 802.22, a
performance evaluation of the protocols of the present invention
were conducted. The simulation parameters included sharing a single
channel in which each superframe is comprised of 16 frames. Each
frame within the superframe is 10 ms in length and the
self-coexistence window is 1 ms. The simulations were conducted
over a 10,000 second period of time.
Three coexistence scenarios were examined including a complete
graph scenario, a cycle graph scenario and a wheel graph scenario.
FIG. 12 shows a graphical representation of various coexistence
scenarios used in the simulation evaluation. Each graphical
depiction identifies a plurality of the stations or WRAN cells and
their respective communication paths.
The first coexistence scenario examined under the simulation
conditions described above was a complete graph scenario comprised
of four base stations. As shown in FIG. 12a 1210 each of the four
base stations can communicate with the other three base stations in
the complete graph scenario. Thus, the scenario represents a
situation where the WRAN cells of each station overlap. The result
of the simulation, shown in the table below, identify the fairness
of the frame-based, on-demand spectrum contention protocol of the
present invention. For example, theoretically, a perfectly fair
sharing of a spectrum resource between two cells would result in a
0.5 usage of the spectrum for each cell. As shown in the table
below, the present invention identifies that in a two cell scenario
the first cell gained access to the shared spectrum 0.500884 times
as compared to sell two which had access to the shared spectrum of
0.494989. And as shown in the last column, it took 30 seconds to
achieve convergence of this equality.
The remaining entries in the table indicates scenarios of 3, 4, and
5 cell networks. Again, for example, and in correspondence with the
depiction of a complete graph scenario shown in FIG. 12a 1210, a
four cell complete graph scenario experienced convergence within
270 seconds. Each of the four cells achieved approximately 1/4 of
the total access to the shared spectrum. The entries under cell 1,
cell 2, cell 3 and cell 4 represent the actual access to the shared
spectrum for each of the representative cells. Thus, after 270
seconds, with respect to the total access to the shared spectrum,
cell 1 achieved a 0.248409 portion, cell 2 achieved a 0.251128
portion, cell 3 achieved a 0.251106 portion and cell 4 achieved a
0.246233 portion.
TABLE-US-00006 No. of Convergence Cells Cell 1 Cell 2 Cell 3 Cell 4
Cell 5 Optimal Time(s) 2 0.500884 0.494989 1/2 30 3 0.331630
0.329914 0.335365 1/3 150 4 0.248409 0.251128 0.251106 0.246233 1/4
270 5 0.202269 0.193133 0.203893 0.198870 0.198137 1/5 300
Table 1: Complete Graph Scenario
The second performance evaluation of the present invention involved
a cycle graph scenario. As shown in FIG. 12b, a cycle graph
scenario is one in which a plurality of the WRAN cells overlap with
the communication paths being limited. The depiction shown in FIG.
12b is of 5 overlapping WRAN cells in which any one WRAN cell
overlaps with only two one-hop neighbors.
The evaluation of the cycle graph scenario shown in FIG. 12b 1220
demonstrates the convergence occurs more quickly for combinations
of WRAN cells that can be grouped. For example, the convergence of
three WRAN cells occurs in 150 seconds while the convergence of 6
WRAN cells occurs in 30 seconds. Correspondingly, the convergence
of five WRAN cells occurs in 336 seconds. The reason for this is
because six WRAN cells can be grouped into three sets of two WRAN
cells and similarly four WRAN cells can be grouped into two sets of
two WRAN cells. However, numbers such as five and seven WRAN cells
cannot be grouped efficiently thus resulting in a higher
convergence time. (See below)
TABLE-US-00007 No. of Convergence Cells Cell 1 Cell 2 Cell 3 Cell 4
Cell 5 Cell 6 Cell 7 Optimal Time(s) 3 0.331630 0.329914 0.335365
1/3 150 4 0.501248 0.495934 0.495934 0.500581 1/2 32 5 0.420031
0.284119 0.419478 0.416048 0.4197 336 6 0.497953 0.498706 0.497822
0.498873 0.497619 0.4989 1/2 30 7 0.430724 0.448526 0.428689
0.436894 0.439151 0.432226 0.348478 3/7 418
Table 2: Cycle Graph Scenario
As with the simulation scenario involving a complete graph, a cycle
graph scenario also provides equitable results. For example, in the
cycle graph of 3 WRAN cells each achieves access to approximately
1/3 of the shared spectrum. As shown above, cell 1 achieves a
0.331630 portion access, cell 2 achieves a 0.329914 portion access
and cell 3 achieves a 0.335365 portion access to shared spectrum.
In a four cell example, access is based on a two cell grouping.
Thus, for an equitable distribution of the shared spectrum any one
cell should achieve approximately a 0.5 portion access to the
shared spectrum. As can be seen in the results shown in the table
above, each cell in a four cell scenario achieves approximately a
0.5 portion access to the shared spectrum and does so with a
convergence of approximately 32 seconds. Similar equitable results
can be seen for scenarios of 5, 6 and 7 WRAN cell networks.
The final scenario for the performance evaluation of a frame-based,
on-demand spectrum contention protocol is that of a wheel graph
scenario 1230. A wheel graph scenario is one of the plurality of
WRAN cells in which each cell overlaps with and can communicate
with each other cell. Again, as with the cycle graph scenario,
convergence is optimized when cells can be grouped. For example a
five WRAN cell scenario can be optimized by examining the
convergence of groups of three WRAN cells.
TABLE-US-00008 No. of Convergence Cells Cell 1 Cell 2 Cell 3 Cell 4
Cell 5 Cell 6 Cell 7 Optimal Time(s) 4 0.248409 0.251128 0.251106
0.246233 1/4 270 5 0.334881 0.333089 0.32877 0.334587 0.327745 1/3
505 6 0.283983 0.277948 0.305698 0.278366 0.283266 0.278926 2/7
1933 7 0.324517 0.335407 0.336619 0.330762 0.330051 0.329977
0.331971 1/3 1112
Table 3: Wheel Graph Scenario
Table 3 above shows that an optimal conversion of four WRAN cells
in a wheel graph scenario is approximately 1/4 of the shared
spectrum. Thus, each of the 4 WRAN cells should gain approximately
a 0.25 portion access to the shared spectrum upon convergence. The
result of the simulation above shows that after 270 seconds, cell 1
achieved a 0.248409 portion access, cell 2 achieved a 0.251128
portion access, cell 3 achieved a 0.251106 portion access and cell
4 achieved a 0.246233 portion access to shared spectrum. Similarly,
in a five WRAN cell wheel graph scenario, the optimal convergence
occurs by a grouping of three cells. Thus, each of the three
grouped cells should achieve approximately a 1/3 portion access to
the shared spectrum upon convergence. The result of the simulation
shows that in a five cell wheel graph scenario, cell 1 achieved a
0.334881 portion access, cell 2 achieve a 0.333089 portion access,
cell 3 achieved a 0.328770 portion access, cell 4 achieved a
0.334587 portion access and cell 5 achieved a 0.327745 portion
access with a total convergence time of 505 seconds.
The present invention presents a frame-based, on-demand spectrum
contention protocol which is both fair and efficient. Evaluations
under a simulation tool have shown that the protocol of the present
invention provides a rapid and fair allocation of a limited
resource in a cognitive radio system. This allocation is on-going
so as to prevent any interruption of data services and is further
scalable to meet the needs of an expanding network.
The prior description has primarily used the example of three
overlapping base stations in which a contention has arisen for use
of a shared spectrum resources by two of three WRANs. As mentioned,
the embodiments of the present invention described herein are
scalable and are equally adept to complicate CR communication
systems. FIG. 13 shows a series of five overlapping WRAN cells
which are vying for control and access of a limited shared spectrum
resource using one embodiment of a frame-based, on-demand spectrum
contention protocol of the present invention.
To better understand the methodologies presented herein assume, as
before, that a shared spectrum resource, one or more frames of a
superframe, is being occupied by Network 2 1320. Further assume
that all five WRANs depicted exist within the incumbent TV area
1360 and only limited portions of a single channel are available
for CR use. In this example, Network 2 1320 is exclusively using
available frames 2, 5 and 8 while the incumbent utilizes frames 1,
6, 7, and 9-16. Thus, WRAN 1 1310 and Network 3 1330 can, at this
time, only use frames 3 or 4. If Network 3 1330 is using only frame
4, Network 4 1340 is free to use frames 2, 3, 5, and 8.
Network 1 1310 may experience an internal increase in demand (the
addition of more CPE in its area of responsibility) causing it to
seek additional spectrum resources. From Network 2's 1320
perspective, the internal demand on Network 1 1310 is seen as an
external demand. Accordingly, Network 1 1310, seeing that there are
no unoccupied frames in the shared spectrum resource, targets at
least one of frames 2, 5 or 8 to meet its demand. For this example,
assume Network 1 1310 is targeting frame 5.
Just as the contention protocol proceeds as previously discussed at
Network 2 1320 with respect to frame 5, a concurrent contention can
be taking place at Network 4 1340. Network 5 1350 may have
initiated a contention for some of the shared spectrum resources
controlled by Network 4 1340. For example, Network 5 may be
targeting frames 4 and 5. From Network 5's 1350 perspective frame 4
is unoccupied and it can be acquired without contention.
Frame 5, however, is occupied by Network 4 1340 resulting in a
contention. During the period of time governed by the length of the
superframe in which the contention for frame 5 is decided by
Network 2 1320, the contention for frame 5 is also determined by
Network 4 1340. The superframes, during which the independent
decisions are made, are synchronized. It is possible for Network 4
1340 to lose the contention thus releasing to Network 5 1350
control of frame 5 while at the same time Network 2 wins the
contention retaining use of frame 5. In such a scenario, Network 3
1330 is still precluded from acquiring frame 5 even though Network
4 1340 released frame 5. Each WRAN cell must independently
determine its topology of one-hop neighbors and shared spectrum
resource utilization to determine which frames are available and
which are not and the distribution of occupancy of the frames can
change (and often does) upon determination interval (e.g.
superframe). Over time, access to the shared spectrum is
equitable.
In a preferred embodiment, the present invention can be implemented
in software and executed on devices having a microprocessor such as
a computer, cellular telephone, personal data assistant, and the
like. Software programming code which embodies the present
invention is typically accessed by a microprocessor from long-term,
persistent storage media of some type, such as a flash drive or
hard drive. The software programming code may be embodied on any of
a variety of known media for use with a data processing system,
such as a diskette, hard drive, or CD-ROM. The code may be
distributed on such media, or may be distributed from the memory or
storage of one computer system over a network of some type to other
computer systems for use by such other systems. Alternatively, the
programming code may be embodied in the memory of the device and
accessed by a microprocessor using an internal bus. The techniques
and methods for embodying software programming code in memory, on
physical media, and/or distributing software code via networks are
well known and will not be further discussed herein.
Generally, program modules include routines, programs, objects,
components, data structures and the like that perform particular
tasks or implement particular abstract data types. Moreover, those
skilled in the art will appreciate that the invention can be
practiced with other computer system configurations, including
hand-held devices, multi-processor systems, microprocessor-based or
programmable consumer electronics, network PCs, minicomputers,
mainframe computers and the like. The invention may also be
practiced in distributed computing environments where tasks are
performed by remote processing devices that are linked through a
communications network. In a distributed computing environment,
program modules may be located in both local and remote memory
storage devices.
An exemplary system for implementing the invention includes a
general purpose computing device in the form of a conventional
computer, a personal communication device or the like, including a
processing unit, a system memory, and a system bus that couples
various system components including the system memory to the
processing unit. The system bus may be any of several types of bus
structures including a memory bus or memory controller, a
peripheral bus, and a local bus using any of a variety of bus
architectures. The system memory generally includes read-only
memory (ROM) and random access memory (RAM). A basic input/output
system (BIOS), containing the basic routines that help to transfer
information between elements within the personal computer, such as
during start-up, is stored in ROM. The personal computer may
further include a hard disk drive for reading from and writing to a
hard disk and a magnetic disk drive for reading from or writing to
a removable magnetic disk. The hard disk drive and magnetic disk
drive are connected to the system bus by a hard disk drive
interface and a magnetic disk drive interface respectively. The
drives and their associated computer-readable media provide
non-volatile storage of computer readable instructions, data
structures, program modules and other data for the personal
computer. Although the exemplary environment described herein
employs a hard disk and a removable magnetic disk, it should be
appreciated by those skilled in the art that other types of
computer readable media which can store data that is accessible by
a computer, such as magnetic cassettes, flash memory cards, digital
video disks, random access memories (RAMs), read-only memories
(ROMs) and the like may also be used in the exemplary operating
environment.
A number of program modules may be stored on the hard disk,
magnetic disk, ROM or RAM, including an operating system, one or
more application programs or software portions, other program
modules and program data. A user may enter commands and information
into the personal computer through input devices such as a keyboard
and pointing device. Other input devices may include a microphone,
joystick, game pad, satellite dish, scanner or the like. These and
other input devices are often connected to the processing unit
through a serial port interface that is coupled to the system bus,
but may be connected by other interfaces, such as a parallel port,
game port or universal serial bus (USB). A monitor or other type of
display device may also be connected to the system bus via an
interface, such as a video adapter.
A computer implementing one or more embodiments of the present
invention may operate in a networked environment using logical
connections to one or more remote computers, such as a remote
computer. The remote computer may be another personal computer, a
server, a router, a network PC, a peer device or other common
network node, and typically includes many or all of the elements
described above relative to the personal computer. The logical
connections described herein include LAN and wide area networks
(WAN). Such networking environments are commonplace in offices,
enterprise-wide computer networks, Intranets and the Internet.
When used in a LAN networking environment, the personal computer is
connected to the local network through a network interface or
adapter. When used in a WAN networking environment, the personal
computer typically includes a means for establishing communications
over the wide area network, such as the Internet. This means is
connected to the system bus via the serial port interface. In a
networked environment, program modules depicted relative to the
personal computer, or portions thereof, may be stored in the remote
memory storage device. It will be appreciated that the network
connections shown are exemplary and other means of establishing a
communications link between the computers may be used.
As will be understood by those familiar with the art, the invention
may be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. Likewise, the
particular naming and division of the modules, managers, functions,
systems, engines, layers, features, attributes, methodologies, and
other aspects are not mandatory or significant, and the mechanisms
that implement the invention or its features may have different
names, divisions, and/or formats. Furthermore, as will be apparent
to one of ordinary skill in the relevant art, the modules,
managers, functions, systems, engines, layers, features,
attributes, methodologies, and other aspects of the invention can
be implemented as software, hardware, firmware, or any combination
of the three. Of course, wherever a component of the present
invention is implemented as software, the component can be
implemented as a script, as a standalone program, as part of a
larger program, as a plurality of separate scripts and/or programs,
as a statically or dynamically linked library, as a kernel loadable
module, as a device driver, and/or in every and any other way known
now or in the future to those of skill in the art of computer
programming. Additionally, the present invention is in no way
limited to implementation in any specific programming language, or
for any specific operating system or environment. Accordingly, the
disclosure of the present invention is intended to be illustrative,
but not limiting, of the scope of the invention, which is set forth
in the following claims.
While there have been described above the principles of the present
invention in conjunction with a frame-based, on-demand spectrum
contention protocol, it is to be clearly understood that the
foregoing description is made only by way of example and not as a
limitation to the scope of the invention. Particularly, it is
recognized that the teachings of the foregoing disclosure will
suggest other modifications to those persons skilled in the
relevant art. Such modifications may involve other features that
are already known per se and which may be used instead of or in
addition to features already described herein. Although claims have
been formulated in this application to particular combinations of
features, it should be understood that the scope of the disclosure
herein also includes any novel feature or any novel combination of
features disclosed either explicitly or implicitly or any
generalization or modification thereof which would be apparent to
persons skilled in the relevant art, whether or not such relates to
the same invention as presently claimed in any claim and whether or
not it mitigates any or all of the same technical problems as
confronted by the present invention. The Applicant hereby reserves
the right to formulate new claims to such features and/or
combinations of such features during the prosecution of the present
application or of any further application derived therefrom.
* * * * *